1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and an apparatus for cell search and synchronization for a subscriber station of the Long Term Evolution (LTE) system. In the LTE system, a base station will transmit a specific primary synchronization signal in each frame to allow a subscriber station to detect the cell arrangement in the LTE system, thereby establishing system synchronization. The method proposed by the present invention can accurately and effectively detect various primary synchronization signals used by different base stations and simultaneously complete system synchronization and the detection of the integer carrier frequency offset (ICFO).
2. Description of the Prior Art
Currently, various communication standards, such as E-UTRA (the abbreviation for evolved UMTS Terrestrial Radio Access), also referred to as Long Term Evolution (LTE), have been developed to provide relatively high data rate so as to support high quality services. LTE is a 3rd Generation Partnership Project (3GPP) standard that provides for an uplink speed of up to 50 Mbps and a downlink speed of up to 100 Mbps. The LTE/E-UTRA standard represents a major advance in cellular technology. The LTE/E-UTRA standard is designed to meet current and future carrier needs for high-speed data and media transport as well as high-definition video support. The LTE/E-UTRA standard brings many technical benefits to cellular networks, some of which include the benefits provided by Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) data transmission.
An OFDM system is characterized by high spectrum efficiency, frequency selective fading resistance, multipath fading resistance, inter-symbol interference (ISI) resistance and adaptive transmission mechanism, and is capable of using a simple frequency domain equalizer (FDE) as data recovery of a receiver. In addition, in the LTE system, Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier-Frequency Division Multiple Access (SC-FDMA) are used on the downlink (DL) and on the uplink (UL), respectively.
Mobility management represents an important aspect of the LTE/E-UTRA standard. As a mobile device, also called user equipment (UE) in the LTE/E-UTRA standard, moves within an LTE/E-UTRA coverage area, the transmission of synchronization signals and cell search procedures provide a basis for the mobile device or UE to detect and synchronize with individual cells. To communicate with a particular cell, mobile devices in associated LTE/E-UTRA coverage area need to determine one or more cell specific transmission parameters such as symbol timing, radio frame timing, and/or a cell identification (ID). In the LTE/E-UTRA standard, the cell-specific information is carried by reference and synchronization signals. The latter forms the basis for DL synchronization and cell specific information identification at the mobile devices within the associated LTE/E-UTRA coverage area. Two DL synchronization signals, namely Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS), are used to allow the mobile devices to synchronize with the transmission of the particular cell, thereby obtaining cell specific information.
The traditional synchronization technique for the LTE system detects the primary synchronization signal based on a joint detection of the unique identification to which the primary synchronization signal corresponds and the ICFO. Traditional methods are complicated and require a huge amount of hardware resource. Moreover, the robustness of traditional detection techniques in resisting frequency selective fading caused by the wireless channel is poor, thus the accuracy of the detection and the communication quality are compromised. Therefore, the above-mentioned traditional methods still have many defects and need to be improved.
In view of the above-mentioned defects in traditional methods, the inventor endeavors to develop a method and an apparatus for cell search and synchronization for a subscriber station of the LTE system.